Bright anodized aluminum alloy



United States Patent 3,530,048 BRIGHT ANODIZED ALUMINUM ALLOY GeorgeRichard Darrow, Richmond, Va., assignor to Reynolds Metals (lompany,Richmond, Va., a corporation of Delaware No Drawing. Filed Feb. 8, 1968,Ser. No. 703,897 Int. (ll. C23b 9/02 US. Cl. 20433 11 Claims ABSTRACT OFTHE DISCLOSURE A bright anodized article, such as a golf club shaft, ofan aluminum alloy of the 7000 series, is produced by preconditioning thealloy prior to heat treatment, by subjecting the alloy to a coldmechanical work of at least 40%, followed by application of adeoxidizing bath. The alloy is then heat treated, the surface deoxidizedagain, chemically brightened by an aluminum phosphate bath at elevatedtemperature, and finally anodized and sealed.

BACKGROUND OF THE INVENTION The most widely used material for metal golfclub shafts has been chromium-plated steel. This material has certaindrawbacks, however, principally that of weight. Many efforts have beenmade in the past to adapt aluminum to golf club shaft requirements,since aluminum produces a lighter shaft under the same playingconditions and this enables the golf club designer to produce a clubwhich will drive the golf ball further. Aluminum golf club shafts havenot come into general use in the past, however, because until recentlyaluminum alloys having the requisite high strength and brightnessapproximating that of the conventional steel shafts were not available.

Aluminum alloy golf club shafts are in the form of hollow tubes made byextruding, drawing and tapering to get the desired shape. The length ofthe shaft ranges from 31 inches to 48 inches, the outside diameter fromabout 0.390 inch to 0.6 inch, and the wall thickness from about 0.032inch to 0.065 inch.

Certain aluminum alloys of the 7000 series (Aluminum Associationdesignation) have been found to be the most suitable for this purpose,particularly in regard to their favorable stress-corrosion resistanceand high mechanical strength. The high strength alloys contain from 1.6to 2.6 percent copper, 2.4 to 3.4 percent magnesium, 6.3 to 8.0 percentzinc, and small amounts of other elements such as silicon, iron,chromium and titanium.

The alloy of this series which is 'best suited for golf club shaft usebecause of its high strength and a minimumof stress-corrosion problemsis alloy 7178, which has the nominal composition, in percentages byweight:

Copper 1.6-2.4 Magnesium 2.4-3.1 Zinc 6.3-7.3 Silicon 0.50 Iron 0.7Manganese 0.30 Chromium 0 l80.40 Titanium 0.20 Other 0.05 AluminumBalance For golf club shaft purposes the drawn and tapered shaft madefrom the 7000 series alloy must be subjected to solution heat treatment,quenching and aging suitable for the particular alloy, then mechanicallyor chemically polished, and finally anodized, to produce a bright finishon the outer surface.

Efforts to utilize alloys of the 7000 series in this way 353,048Patented Sept. 22, 1970 ICC have been unsuccessful in the past becausethe color and appearance of the heat treated and anodized shaft wereunsatisfactory. The finished shafts exhibited a greyish pewter color,with a broken surface. This condition was believed attributable to thehigh copper and zinc content of these alloys and to the effects of theheat treatment. Attempts to improve he appearance by chemical polishingof the heat treated surface were likewise unsuccessful, because usuallyslight etching of the surface rather than brightening took place, andthis further impaired the appearance of the final product. Anotherdrawback was that even after anodizing, the anodic coating would becomegrey and lose whatever brightness it originally had.

It was accordingly the principal object of the invention to produce analuminum alloy shaft for golf clubs or the like (e.g., ski poles), Whichcould be heat treated, polished and anodized to a lasting bright finish.

Another object was to produce a bright finished golf club shaft from analloy of the 7000 series, and particularly alloy 7178.

SUMMARY OF THE INVENTION In accordance with one aspect of the presentinvention, it has been found that adverse effects of heat treatment ofaluminum alloys of the 7000 series can be avoided or minimized bysubjecting the alloy to at least 40% cold Work from zero temper prior tothe heat treatment. In the case of a golf club shaft, the extrusion isusually annealed to zero temper and then cold work is imparted bydrawing and tapering the extrusiondown to final shape. Thus, forexample, a 1 inch outside diameter tube drawn down to 0.6 inch outsidediameter represents approximately a 40% reduction, which is typical forthe large end of the shaft. Additional cold work may be imparted bytapering the small end of the shaft down to 0.39 inch outside diameter,representing a 60% reduction at the small end of the shaft. The shaftmay have a straight or stepped taper, with progressively increased coldwork. toward the small end of the shaft.

The foregoing cold work conditioning treatment permits the subsequentheat treatment to be performed so as to obtain the required minimumphysical properties in the alloy, while at the same time imparting tothe heat treated alloy the capability of accepting polishing treatment,and eventual anodizing to a. bright finish, free from discoloration andsurface blemishes.

In accordance with a second aspect of the invention, it has been foundadvantageous to subject the cold worked alloy to a deoxidizing treatmentprior to the heat treatment. This further conditions the shaft for heattreatment, and constitutes a surprising and unexpected improvement,because these alloys are normally susceptible to corrosion, and it wasthe prevailing practice to leave the natural oxide film on the alloysurface before heat treating to protect it from corrosion during theheating and quenching steps.

The deoxidizing treatment is performed by immersing the article in anacid bath containing a mineral acid, such as sulfuric acid, and eitherchromic acid, or an alkali metal chromate, or dichromate, or bisulfate.Suitable alkali metals include sodium and potassium. Thus, the range ofconcentration of the sulfuric acid may lie between about 7.5% and 9.0%by weight, and that of the chromic acid or equivalent constituentbetween about 2.5% and about 3.5%, the remainder of the bath beingWater. A suitable deoxidizing bath is an aqueous solution of 3% CrO and8% H by weight, which is applied at a temperature between about 70 F.and F. This bath dissolves the aluminum. oxide film. The dip is followedby a warm water F. or more) rinse to dry the metal surface prior to heattreatment. The heat treating step should be performed within about 6hours of deoxiding.

Thus, in accordance with the invention, the preconditioning cold worktreatment and the deoxidizing treatment cooperate to produce anunexpected improvement in the heat treatment and especially in thebright anodizing response of the alloy.

While the process of the present invention is applicable to the aluminumalloys of the 7000 series generally, such as, for example, alloys 7001,7075, 7079, 7175 and 7178, it is particularly well adapted to theimprovement of alloy 7178. Accordingly, the description of the processwill be illustrated with respect to alloy 7178, but it is to beunderstood that the general sequence of steps is applicable to the otheralloys of the series, with appropriate variations depending upon theparticular alloy being treated.

The types of heat treatment for the individual alloys of the 7000 seriesare known and do not constitute a part of the present invention.Typically, solution heat treatment takes place at between 820 F. and 950F. In the case of 7178 alloy, for example, the solution heat treatmentis performed at a temperature between 860 F. and 930 F., preferably at870 F.::l F. for about 20 minutes. This is followed by quenching inwater at a temperature of about 90 F. or lower, within 1 to a maximum of5 seconds. For best results, the 5 second limit is critical. The articleis then aged at about 240 F. to about 260 F., preferably at 250 F.i5 F.for 24 hours.

Following the heat treatment, the article is again deoxidized to removeall naturally formed oxide and heat treatment scale. The deoxidizingstep is performed with the same type of bath as employed in the previousdeoxidizing treatment, and it greatly contributes to the clarity of theanodic film subsequently formed on the shaft.

The aluminum alloy article may thereafter be subjected to mechanicalfinishing, such as surface buffing or polishing, to impart an acceptabledegree of surface luster.

In order to maintain and improve the final brightness of the anodizedarticle, while allowing for cleaning of the surface, the shaft is thensubjected to a chemical brightening treatment using an acid bath ofspecially selected type which will not diminish but improve thespecularity of the surface, and which contains aluminum phosphate as anactive chemical reaction limiting ingredient. Aluminum phosphate acidbaths have been known in the prior art for the brightening of automotivetrim. They contain about 6% to 7% by weight of aluminum phosphate orless, together with surfactants, and are conventionally applied attemperatures in the range of 190 F. to 210 F. These automotive typebathsproved unsuited for aluminum alloy golf club shaft treat ment.

In accordance with the present invention, it was found that by employinga special aluminum phosphate brightening bath, the specularity of thearticle would be improved, and the anodizing effect would be enhanced.The bath composition must be carefully controlled, the following rangesof composition being critical:

Aluminum phosphate Al (PO 910% by weight Nitric acid HNO 3-3.5 by weightPhosphoric acid H PO 65-70% by weight Copper added as sulfate:0.00150.0025% by weight Water: 18-21% No surfactants are employed, andthe bath is applied to the article at a temperature between about 225 F.and 230 F. for a period of time between about 1.3 and 1.7 minutes. Thealuminum phosphate can be incorporated as such, or can be formed in situby using aluminum hydroxide as an ingredient.

The article is then ready for anodizing. This step is performed inaccordance with conventional practice, employing a mineral acidelectrolyte, preferably sulfuric acid at a concentration between about12% and 20% by weight, for example 15%. Anodizing temperature liesbetween about 70 F. and F., preferably 75 F.:1 F. Current density rangefrom about 10 to 15, and preferably 12 amperes per square foot.Anodizing time is sufficient to produce an oxide film of 0.10 to 0.45mil thickness, preferably 0.20 mil. After anodizing the anodic coatingis sealed by treatment with hot water, preferably deionized water, at atemperature between about 206 F. and 211 F. for at least 15 minutes. ThepH of the water should be adjusted to between 6.0 and 6.5, by additionof a small amount, e.g. 4 p.p.m. of a phosphate buffer, and 1000 ppm. ofsodium acetate.

Thus, there is within contemplation of the present invention thepreconditioning of the aluminum alloy article before heat treatment, andcomprising the steps of subjecting the article to a cold mechanical sizereduction of at least 40%, followed by deoxidizing the surface of thealloy. The invention also includes the entire sequence of brightanodizing an aluminum alloy article, such as a golf club shaft, by heattreating the previously cold worked and deoxidized alloy, followed bychemical brightening, anodizing, and optionally, sealing the anodizedarticle.

DESCRIPTION OF THE PPREFERRED EMBODIMENT The following exampleillustrates a present preferred practice of the invention:

Example An extruded tube of 7178 aluminum alloy having an outsidediameter of 1 inch was cold drawn down to 0.6 inch outside diameter, andfurther drawn down to 0.39 inch, representing a reduction of about 60%.The tube was then deoxidized by applying to the surface an aqueoussolution containing 8% H SO and 3% CrO by weight to dissolve the oxidefilm. This treatment was followed by a warm water rinse at 160 F. andthe metal surface was allowed to dry. The tube was then solution heattreated at 870 F.il0 F. for 20 minutes, then quenched in water at F.within 5 seconds after leaving heat treatment, and then aged for 24hours at 250 Fi-5 F. The tube was again deoxidized with the samedeoxidizing solution, and then mechanically buffed to a good surfaceluster. The article was then chemically brightened by immersion in asolution containing 9% Al (PO 3% HNO 18% H 0, 65% H PO and 0.0015%copper added as sulfate, at 225 F. for 1.5 minutes. The article wasrinsed and anodized in 15% sulfuric acid at 75 F.:1 F. at 12 amperes persquare foot current density until an oxide film of 0.14 mil thicknesswas obtained. The coating was then sealed with deionized water with 3ppm. phosphate added and buffered to pH 6.0. The resulting coating waslustrous and attractive.

While present preferred embodiments of the invention have beendescribed, and have been further illustrated by by an example, it willbe recognized that the invention may be otherwise variously embodied andpracticed within the scope of the following claims.

What is claimed is:

1. Process of producing a bright anodized article of an aluminum alloyof the 7000 series, comprising the steps of:

(a) subjecting said article to a cold mechanical size reduction of atleast 40%;

(b) deoxidizing the surface of the alloy by applying to the article abath containing a mineral acid and a member selected from the groupconsisting of chromic acid, an alkali metal chromate, an alkali metaldichromate, and an alkali metal bisulfate;

(c) solution heat treating, quenching, and aging the article;

(d) deoxidizing the surface of the heat treated alloy by applying to thearticle the bath recited in step (e) chemically brightening the surfaceof the article by applying thereto an aqueous solution of thecomposition: Al (PO 910%, HNO 3-3.5%, H PO 65-70%, H O 18-21%, copperadded as sulfate 0.00l50.0025%, percentages being by weight, at atemperature between about 225 F. and 230 F.; and

(f) anodizing the article.

2. The process of claim 1 in which the alloy is 7178 alloy.

3. The process of claim 1 in which the article is a tubular extrusion.

4. The process of claim 1 in which the article is a golf club shaft.

5. The process of claim 1 in which the mechanical size reduction is madeby cold drawing.

6. The process of claim 1 in which the deoxidizing bath consistsessentially of sulfuric acid and chromic acid.

7. The process of claim 1 in which the article is memechanicallyfinished to acceptable surface luster following the second deoxidizingstep.

8. The process of claim 1 in which the anodized coating is sealed withhot Water.

9. A bright anodized 7178 aluminum alloy golf club shaft producedaccording to the process of claim 1.

10. Process of producing a bright anodized tubular article of analuminum alloy of the 7000 series, comprising the steps of (a) forming atubular extrusion of said alloy;

(b) annealing said tubular extrusion to zero temper;

(0) drawing and tapering said extrusion to effect a cold mechanical sizereduction of at least 40%;

(d) deoxidizing the extrusion by applying to the surface a bathcontainign a mineral acid and a member selected from the groupconsisting of chromic acid,

an alkali metal chromate, an alkali metal dichromate, and an alkalimetal bisulfate;

(e) solution heat treating the extrusion at a temperature between about860 F. and about 930 F.;

(f) quenching at a temperature not above about 90 F. for a maximum of 5seconds;

(g) aging at a temperature of about 240 F. to about (h) deoxidizing thearticle as in step (d);

(i) subjecting the article to mechanical polishing;

(j) chemically brightening the surface of the article by applyingthereto an aqueous solution of the composition: Al (PO 9-10%, HNO3-3.5%, H PO -70%, H O 18-21%, copper added as sulfate 0.00150.0025%,percentages being by weight, at a temperature between about F. and F.and at a current density from about 10 to 15 amperes per square foot.

11. The process of claim 10 in which the article is a golf club shaft.

References Cited UNITED STATES PATENTS Re. 26,216 5/1967 English 20458XR 2,941,930 6/1960 Mostovych et al 204-29 3,180,806 4/ 1965Hollingsworth 20429 3,351,442 11/1967 Hooper 204-29 XR FOREIGN PATENTS763,549 12/ 1956 Great Britain.

DANIEL E. WYMAN, Primary Examiner P. E. KONOPKA, Assistant Examiner US.Cl. X.R..

